The invention concerns a flowmeter of a type shown in U.S. Pat. No. 2,209,700 as a component of a gasoline pump. In the known flowmeter, the rotor is comparable to the many-bladed wheel of a turbine and is provided at its circumference with an annular disk extending into an annular chamber starting radially from the cylindrical passage with which it communicates. This chamber is bounded by end walls comprising mutually aligned windows. The disk also has two windows. Furthermore, a light barrier is flush with the windows in the end walls, its beam being parallel to the rotor axis. Upon every revolution of the rotor, one of the windows in the annular disk moves past the windows in the end walls and thereby releases the light barrier beam to generate a count signal.
The known flowmeter suffers from several drawbacks. Its response is comparatively sluggish because the rotor must overcome the hydraulic friction between the annular disk on one hand and the two end walls of the chamber on the other, both when being set into and when continuing its rotation. The sluggishness of the known flowmeter furthermore degrades its accuracy if the flow must be suddenly stopped because the comparatively large mass of the rotating rotor plus annular disk causes the latter to go on rotating somewhat even when the liquid flows no longer. These drawbacks of the known flowmeter further are the cause of its characteristics being hardly linear in the sense of the number of rotor revolutions being rigorously proportional to the flow quantity. Such drawbacks, however, are of little significance in the known flowmeters because the flow quantity as a rule varies only within relatively narrow limits in gasoline pumps.
Moreover, the known flowmeter is not highly precise because only two count signals are generated for each revolution, each being essentially sinusoidal. Lastly, the known flowmeter is unsuitable for very small flow rates because its dimensions cannot be shrunk at will.
Accordingly, it is the object of the invention to so design a flowmeter of the initially cited species that the mentioned drawbacks are avoided and that the flowmeter can be made so small that flow rates of about 0.5 liters per hour still can be measured very accurately.